Add Stim MPP stabilizer import

[masa10-f]

Summary

• Add graphqomb.qec.stim_mpp utilities for extracting StabilizerCode inputs from Stim MPP layers.
• Preserve sparse Stim qubit ids via dense-column mappings and import qubit coordinates.
• Add optional graphqomb[stim] dependency metadata and lockfile entries.
• Document the feature in CHANGELOG.md.

Validation

• env PYTHONPATH=/home/masa10/git-repos/utftbmqc/ls-pattern-compile:/home/masa10/git-repos/utftbmqc/graphqomb uv run --no-sync ruff check
• env PYTHONPATH=/home/masa10/git-repos/utftbmqc/ls-pattern-compile:/home/masa10/git-repos/utftbmqc/graphqomb uv run --no-sync pytest -q
• env PYTHONPATH=/home/masa10/git-repos/utftbmqc/ls-pattern-compile:/home/masa10/git-repos/utftbmqc/graphqomb uv run --no-sync pyright graphqomb/qec/stim_mpp.py tests/test_stim_mpp.py

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Handle inverted MPP targets instead of dropping signs

When a Stim MPP product uses an inverted target such as MPP !Z5 or X2*!Y3*Z5, Stim flips the recorded measurement result, but this parser treats the target exactly like an uninverted Pauli target and loses that sign/constant offset. For circuits that use these valid MPP forms, the extracted stabilizer and any imported detector/logical parity rows no longer match the Stim circuit; if signs are not representable here, this should at least reject target.is_inverted_result_target instead of silently importing incorrect data.

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